Refining surface for a refiner for defibering material containing lignocellulose

ABSTRACT

The invention relates to a refining surface in a refiner for defibering material containing lignocellulose, which refiner has two coaxially rotating refining surfaces. The material being defibered is fed between the refining surfaces that both have grooves and bars. According to the invention, at least some of the refining surfaces have on their outer surface a bevel that becomes lower starting from the incoming direction of the bars of the other refining surface so that when the refining surfaces rotate relative to each other, a force that pushes the refining surfaces away from each other is created between them.

FIELD OF THE INVENTION

The invention relates to a refining surface in a refiner for defiberingmaterial containing lignocellulose, which refiner has two coaxiallyrotating refining surfaces, between which the material being defiberedis fed and which both have grooves and bars in them.

BACKGROUND OF THE INVENTION

Material containing lignocellulose, such as wood or the like, isdefibered in disc and conical refiners to produce different fibre pulps.Both the disc refiners and the conical refiners have two refiner discswith a refining surface on both of them. The disc refiners have adisc-like refiner disc and the conical refiners have a conical refinerdisc. The refiner discs are mounted with their coaxially rotatingrefining surfaces against each other. Either one of the refiner discsthen rotates relative to a fixed refiner disc, i.e. stator, or bothdiscs rotate in opposite directions relative to each other. The refiningsurfaces of refiner discs typically have grooves and protrusions, orblade bars, between them, called bars in the following. The shape ofthese grooves and bars may vary in many different ways per se. Thus, therefining surface, for instance, may in the radial direction of therefiner disc be divided into two or more circular parts, with groovesand bars of different shapes in each of them. Similarly, the number anddensity of bars and grooves on each circle, and their shape andinclination may differ from each other. Thus, the bars may either becontinuous along the entire radius of the refining surface or there maybe several consecutive bars in the radial direction.

The refiner discs are formed in such a manner that the distance betweenthe refining surfaces is longer in the centre of the refiner discs, andthe gap between the refining surfaces, i.e. refining zone, narrowsoutwards so that processing and defibering the fibre matter in therefiner can be done as desired. Because the material to be defiberedalways contains a significant amount of moisture, a great deal of vapouris generated during defibering, which affects the operation andbehaviour of a disc refiner in many ways.

For controlling the operation of the refiner, it is necessary to be ableto move the refining surfaces to a suitable distance from each other.For this purpose, a loader is typically connected to act on one refinerdisc so as to push the refiner disc towards the second refiner disc orto pull it away from it depending on the internal pressure conditions inthe refiner. The force caused by the pressure between the refiningsurfaces of the refiner can in a normal refiner be negative or positivedepending on for instance vapour pressure, flows of the refiningmaterial affected by the geometry of the refining surfaces,counter-pressure of the refining chamber and many other factors. Thus,when the gap between the refining surfaces in some applications is quitesmall, there is a danger that the refining surfaces touch each other andcause extra wear and possibly even bigger damage. In special situations,in which a low loading force is used and the pressure situation betweenthe discs may change from positive to negative, this risk is quite high.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a refining surfacefor a refiner, by means of which this risk can substantially be avoided.The refining surface of the invention is characterized in that at leastsome of the bars of the refining surfaces have on their outer surface abevel that becomes lower starting from the incoming direction of thebars of the second refining surface so that when the refining surfacesrotate relative to each other, a force that pushes the refining surfacesaway from each other is always created between them.

The essential idea of the invention is that in at least some of the barsof one refining surface, the outer surface of the bar is bevelled insuch a manner that the bevel is in the incoming direction of the bars ofthe second refining surface. This produces a situation, in which thereis always a positive force between the refining surfaces and because ofit, they cannot move towards each other without a separate supportingforce.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described in greater detail in the attacheddrawings, in which

FIG. 1 a cross-sectional schematic view of a conventional disc refiner,

FIG. 2 is a cross-sectional schematic view of a conventional conicalrefiner,

FIG. 3 is a cross-sectional schematic view of a typical refiner discseen from the refining surface,

FIG. 4 a to 4 c are partial schematic cutaway views of a few solutionsof the invention cut in the circumferential direction of the refinerdiscs,

FIG. 5 is a schematic view of the detailed dimensioning of theinvention,

FIGS. 6 a to 6 c are schematic views of a preferred embodiment of theinvention,

FIGS. 7 a to 7 c are schematic views of a second preferred embodiment ofthe invention, and

FIGS. 8 a to 8 c are schematic views of a third preferred embodiment ofthe invention.

FIG. 1 is a cross-sectional schematic side view of a conventional discrefiner. The disc refiner has two coaxially mounted refining surfaces 1and 2. In this embodiment, one refining surface 1 is on a rotatingrefiner disc 3 that is rotated by an axle 4. In this case, the otherrefining surface 2 is on a fixed refiner disc 5, i.e. stator. Therefining surfaces 1 and 2 of the refiner discs 3 and 5 can be eitherformed directly to them or formed of separate refining segments in amanner known per se. Further, FIG. 1 shows a loader 6 that is connectedto act on the refiner disc 3 through the axle 4 in such a manner that itcan be pushed towards the refiner disc 5 to adjust the gap between them.The refiner disc 3 is rotated by the axle 4 in a manner known per se byusing a motor not shown in the figure.

The material containing lignocellulose and being defibered is fedthrough an opening 7 in the middle of one refining surface 2 to the gapbetween the refining surfaces 1 and 2, i.e. the refining zone, where itis defibered and ground while the water in the material is vaporised.The defibered fibre pulp material exits between the refiner discs fromthe outer edge of the gap between them, i.e. the refining zone, to achamber 8 and exits the chamber 8 through an outlet channel 9.

FIG. 2 is a cross-sectional schematic side view of a conventionalconical refiner. The conical refiner has two refining surfaces 1 and 2that form a conical refining zone relative to the centre axis. In thisembodiment, the second refining surface 1 is in a rotating refining cone3 that is rotated by the axle 4. In this case, the other refiningsurface 2 is in a fixed refining cone 5, i.e. stator. The refiningsurfaces 1 and 2 of the refining cones 3 and 5 can be either formeddirectly to them or formed of separate refining segments in a mannerknown per se. Further, FIG. 2 shows a loader 6 that is connected to acton the refining cone 3 through the axle 4 in such a manner that it canbe pushed towards the refining cone 5 to adjust the gap between them.The refining cone 3 is rotated by the axle 4 in a manner known per se byusing a motor not shown in the figure.

The material containing lignocellulose and being defibered is fedthrough an opening 7 in the middle of one refining surface 2 to the gapbetween the refining surfaces 1 and 2, i.e. the refining zone, where itis defibered and ground while the water in the material is vaporised.The defibered fibre pulp material exits between the refiner cones fromthe outer edge of the gap between them, i.e. the refining zone, to achamber 8 and exits the chamber 8 through an outlet channel 9.

FIG. 3 is a cross-sectional schematic view of a typical refining surfaceof a disc refiner seen from the direction of the axle. The refiningsurface has alternately grooves 10 and bars at the same position in thecircumferential direction of the refiner. By way of example, therefining surface is here divided into two radially consecutive circleswith grooves and bars that are different in shape. Thus, the bars in theouter circle can be at least partly curved in the rotating directionshown by arrow A in FIG. 3 so that the material on the outer rim of therefining surface is in a way pumped outwards of the refiner. Refiningsurfaces of this type, which are either formed directly to the refinerdisc or formed of different surface elements in a manner known per se,exist in several forms and can be applied according to the invention.

FIGS. 4 a to 4 c are cross-sectional schematic views in the direction ofthe refiner circumference showing a section of the opposing refiningsurfaces 1 and 2 and the grooves 10 and bars 11 in them. By way ofexample, the refining surface 2 on the right is fixed, i.e. the stator,and the refining surface 1 on the left rotates, i.e. moves in thedirection shown by arrow A in FIGS. 4 a to 4 c relative to the stator.Both refining surfaces can be mobile or rotate coaxially in a mannerknown per se. The refining surfaces are typically vertical and rotatearound a horizontal axle, but the invention can also be applied tosolutions, in which the refining surfaces are horizontal.

FIG. 4 a shows a case, in which there are grooves 10 on a rotatingrefining surface, and bars 11 between the grooves. The bars 11 can havevarious shapes in cross-profile, but in such a manner that in thedirection of travel, there is a bevel 12 which to a certain extent actsas a cutter when the fibres are cut. The second refining surface hasgrooves 20 and bars 21 between them. The grooves 10 and 20 can have manyshapes. In at least some of the bars on the second refining surface 2,the outer surface 22 has a bevel 23 that is convergent, i.e. becomeslower from the incoming direction of the bars 11 of the first refiningsurface towards the back end of the bar 21. Part of the outer surface 22of the bar 21 of the second refining surface 2 can be even so that thefibre material between the bars of the refining surfaces is chafed andground smaller between them. The movement of the refining surfacesrotating relative to each other makes the material being defibered andthe vapour and gas in the disc refiners press between the outer surfacesof the bars 11 and 21 at the bevel 23, which causes an ascending forcethat pushes the refining surfaces away from each other. By suitablyplanning and designing the shape, size and location of the bevels 23 inthe radial direction of the bars produces a situation, in which a forcethat pushes the refining surfaces 1 and 2 away from each other alwaysacts between them. As a result of this, the refining surfaces will nevertouch each other, but try to draw away from each other, and the distancebetween them can easily and reliably be adjusted merely by adjusting thesupporting force of a support apparatus that presses the refiningsurfaces together from the outside.

FIG. 4 b shows an embodiment, in which the bars 11 of a moving rotor 1,i.e. a rotor rotating around an axle, have bevels 13. The operation ofthese corresponds per se to the operation in FIG. 4 a.

FIG. 4 c shows an embodiment, in which the bars 11 and 21 of bothrefining surfaces 1 and 2 have corresponding bevels 13 and 23. This way,the force pushing the refining surfaces away from each other can be madestronger than when the bevel is on the bars of only one refiningsurface.

FIG. 5 is a more detailed schematic view of the dimensioning of theinvention. For the sake of simplicity, it only shows one refiningsurface bar on both sides. It shows the maximum distance H₁ and minimumdistance, i.e. clearance, H₂ between the end surfaces of the bars ofboth refining surfaces.

Several factors affect the magnitude of the force pushing the refiningsurfaces away from each other. These include the mutual speed of therefining surfaces at the bevels of the bars, the amount of material andwater vapour in the refiner, and the dimensions, inclination and shapeof the bevels.

On the basis of the above, it can be established that in certaincircumstances, the maximum force obtained by means of a bevel can bedefined by an expression known from flow dynamics, as disclosed forinstance in B. J. Hamrock, Fundamentals of Fluid Film Lubrication,McGraw-Hill Series in Mechanical Engineering, McGraw-Hill Inc., NewYork, 1994, as follows:

${F_{T} = {\frac{6 \cdot \mu_{ap} \cdot V_{b} \cdot l_{b}^{2}}{\left( {k_{c} - 1} \right)^{2} \cdot H_{2}^{2}} \cdot \left\lbrack {{\ln\left( k_{c} \right)} - \frac{2 \cdot \left( {k_{c} - 1} \right)}{k_{c} + 1}} \right\rbrack}},$

-   -   wherein    -   k_(c)=H₁/H₂ (ratio between the input and output clearances of        the end surfaces of the bars),    -   V_(b)=speed between the refining surfaces, and    -   I_(b)=length of bevel.

The maximum force is obtained by calculating the maximum point of thefunction F_(T) relative to the variable k_(c). The maximum force isobtained with the k_(c) value of 2.2.

$F_{T\mspace{14mu}\max} = {0\text{,}{16 \cdot {\frac{\mu_{ap} \cdot V_{b} \cdot l_{b}^{2}}{H_{2}^{2}}.}}}$

FIGS. 6 a to 6 c show a preferred embodiment of the invention, in whichit has been possible to take into account that when the distance betweenthe refining surfaces changes, the force acting between the refiningsurfaces must change correspondingly as necessary. This embodiment showsby way of example a bar 22 of one refiner disc, which can be either aradial bar along the entire refiner disc or a bar or part of a barforming only a part of it. This embodiment employs a solution, in whichthe bar has three bevels that are different in inclination, and theoperation of each of the bevels is at its most advantageous at aspecific distance between the refining surfaces. This way, when thedistance between the refining surfaces changes, it is possible toutilize the bevel surface that best operates at the distance in questionto achieve the necessary push force. FIG. 6 a shows the embodiment asseen from the surface of the refiner disc, FIG. 6 b shows the topsurface of the bar 22 as seen from the direction of arrow B, and FIG. 6c shows the bar 22 as seen from the direction of arrow C, i.e. from theend of the bar. These show how the bevels are made different atdifferent points along the bar 22. There may be one or more bevels. Inthis solution, there are three bevels.

FIGS. 7 a to 7 c show a second preferred embodiment of the invention.This embodiment shows a similar solution as in FIGS. 6 a to 6 c from thecorresponding directions. However, this embodiment differs from thealternatives shown above in that it is not a combination of consecutivebevels with the same inclination, but the inclination of the bevelchanges from one end of the bar 22 to the other most preferablycontinuously so that the size of the inclination of the bevel 23 changesfrom one end of the bar 22 to the other. For manufacturing, it is ofcourse advantageous to have the highest inclination at one end and thelowest at the other end. Similarly, FIG. 7 b in particular shows thatthe width of the bevel in the transverse direction of the bar 22 is notnecessarily constant, but may vary and can be designed in different waysdepending on the operating conditions.

FIGS. 8 a to 8 c show a third preferred embodiment of the invention.This embodiment shows a similar solution as in FIGS. 6 a to 6 c from thecorresponding directions. However, this embodiment differs from thealternatives shown above in that it is not a combination of consecutivebevels with the same inclination, but the bar 22 has at least twoparallel bevels Ib and Ib′ in the longitudinal direction of the bar 22and the bevels are at different angles as seen from the direction ofarrow C of the bar 22, i.e. from the end of the bar 22.

The solution shown in FIG. 8 c can be formed in such a manner, forinstance, that the entire width I+Ib+Ib′ of the bar 22 is 6.5 mm, inwhich the width of the bevel Ib is 3 mm and the width of the bevel Ib′is 3 mm. When the clearance of the blade surfaces, i.e. the outputclearance H₂, is 0.1 mm by way of example, a preferable input clearanceH₁ according to the invention is 0.22 mm, which is at the same time theoutput clearance H₂′ of a second bevel, which then produces 0.484 mm asthe value of the most preferable input clearance H₁′. The input andoutput clearances are calculated using the expression of the input andoutput clearance ratio described above. The formulas H₁=k_(c)×H₂ andH₁′=k_(c)×H₂′ as applied to this solution have been used in thecalculation. The clearance values are calculated with the input andoutput clearance ratio K_(c) value 2.2 that produces the highestpossible force F_(Tmax) that pushes the refining surfaces away from eachother. By calculating for both partial bevels a force that pushes therefining surfaces away from each other and summing the forces producesthe force opening the refining surfaces of this solution. In thisexample, the distance H₂ between the opposite refining blades is 0.1 mm.The blades can be optimized to a desired blade distance by changing thisvalue, whereby the value of the bevel also changes according to theformula.

The width and length of the bevel in the bars can be designed indifferent ways when the number and location of the bars in the radialdirection of the refining surface and the rotating speed are known, onthe basis of which it is possible to calculate the magnitude of theforce achieved by the bevels and pushing the refining surfaces away fromeach other. Thus, the bevel can be as wide as the entire bar ornarrower. Similarly, the bevel can be as long as the bar or shorter.There may also be bevels in only some of the bars, for instance in everysecond bar, etc. The bevel can be even or convex or concave in thetransverse direction of the bar. Similarly, the bevel can vary in widthin the longitudinal direction of the bar, for instance it can narrowfrom the centre outwards, etc. Even though for achieving the maximumforce, the value for parameter k_(c) is 2.2, it is possible to deviatefrom this value, and a useful range found in practice isk_(c)=2.2+/−50%, preferably k_(c)=2.2+/−20%. Bevels with differentinclinations can also be formed either consecutively in the radialdirection on different bevels or alternately in the circumferentialdirection of the refining surface.

The invention is in the above description and the drawings described byway of example and it is not in any way limited thereto. The essentialthing is that at least in some of the bars of the refining surface,there is a bevel convergently inclined from one edge of the bar to theother on the edge of the bar from which the bars of the other refiningsurface come when the refining surfaces move. The refining surfaces aretypically vertical and rotate around the centre axis, but it is alsopossible to apply the invention to solutions, in which the refiningsurfaces are horizontal. The invention can be applied to twin gaprefiners with a floating rotor, known to persons skilled in the art. Ageneral problem with twin gap refiners is that the blade clearance doesnot remain the same in both refining zones, if there is even a smallflow change in one refining zone. The solution of the inventionstabilizes the operation of the motor and prevents one-side collision ofthe blades. Further, the invention can be applied to low-consistencyrefining and refining the fibres of fibreboard.

1. A refining surface of a refiner, the refiner having two opposedrefining surfaces coaxially-disposed along an axis, with at least one ofthe refining surfaces being configured to rotate about the axis in arotation direction, and the refining surfaces being configured toreceive a lignocellulose material therebetween for defibering thereof,the refining surface comprising: a plurality of radially-extending barsdefining grooves between adjacent bars, each groove having a bottomsurface, and each bar having a leading surface and an opposed trailingsurface with each of the leading and trailing surfaces being configuredto extend away from the bottom surface of the respective grooves, eachbar also having a radially-extending length and an angularly-extendingwidth, at least one of the bars including a non-concave bevel extendingfrom a leading edge of the leading surface of the bar, the leading edgeof the leading surface being defined with respect to the interaction ofthe non-concave bevel with the opposed refining surface, the non-concavebevel being spaced apart from the bottom surface of the groove along theleading surface and extending across the bar, from the leading surface,for less than the entire width thereof, the remainder of the width ofthe bar extending from the non-concave bevel to the trailing surfacebeing substantially parallel to the refining surface, the leading edgeof the non-concave bevel being further configured such that, as anopposed bar of the opposed refining surface approaches axial coincidencewith the non-concave bevel, an increasing force is generatedsubstantially perpendicularly to the refining surface and axiallyoutward with respect to the opposed refining surfaces.
 2. A refiningsurface according to claim 1, wherein less than all of the plurality ofbars includes the non-concave bevel.
 3. A refining surface according toclaim 1 wherein the non-concave bevel is configured so as to define aratio between a maximum clearance (H₁) and a minimum clearance (H₂)between bars of the opposed refining surfaces, H₁/H₂=2.2±50%.
 4. Arefining surface according to claim 1, wherein the ratio isH₁/H₂=2.2±20%.
 5. A refining surface according to claim 3, wherein theratio is H₁/H₂=2.2.
 6. A refining surface according to claim 1, whereinthe non-concave bevel extends for less than the entire length of thebar.
 7. A refining surface according to claim 1, wherein at least one ofthe bars includes a plurality of non-concave bevels, with thenon-concave bevels extending for less than the entire width of the bar,and each non-concave bevel having a different slope with respect to thebar.
 8. A refining surface according to claim 7, wherein the non-concavebevels are serially disposed across the bar, for less than the entirewidth thereof, such that the slope decreases with each non-concavebevel, each non-concave bevel being successively disposed axially inwardwith respect to the opposed refining surfaces.
 9. A refining surfaceaccording to claim 7, wherein the bars spaced apart in an angulardirection about the refining surface alternatingly include non-concavebevels having different slopes.
 10. A refining surface according toclaim 1, wherein at least one of the non-concave bevels defines a slopewith respect to the bar, the slope being configured to vary along thelength of the bar.